On October 10, 2021 7:42:19 AM GMT+02:00, apinski--- via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>From: Andrew Pinski <apin...@marvell.com>
>
>So it turns out this is kinda of a latent bug but not really latent.
>In GCC 9 and 10, phi-opt would transform a?-1:0 (even for signed 1-bit integer)
>to -(type)a but the type is an one bit integer which means the negation is
>undefined. GCC 11 fixed the problem by checking for a?pow2cst:0 transformation
>before a?-1:0 transformation.
>
>When I added the transformations to match.pd, I had swapped the order not
>paying
>attention and I didn't expect anything of it. Because there was no testcase
>failing
>due to this.
>Anyways this fixes the problem on the trunk by swapping the order in match.pd
>and
>adding a comment of why the order is this way.
>
>I will try to come up with a patch for GCC 9 and 10 series later on which fixes
>the problem there too.
>
>Note I didn't include the original testcase which requires the vectorizer and
>AVX-512f
>as I can't figure out the right dg options to restrict it to avx-512f but I
>did come up
>with a testcase which shows the problem and even more shows the problem with
>the 9/10
>series as mentioned.
>
>OK? Bootstrapped and tested on x86_64-linux-gnu.
OK.
Richard.
> PR tree-optimization/102622
>
>gcc/ChangeLog:
>
> * match.pd: Swap the order of a?pow2cst:0 and a?-1:0 transformations.
> Swap the order of a?0:pow2cst and a?0:-1 transformations.
>
>gcc/testsuite/ChangeLog:
>
> * gcc.c-torture/execute/bitfld-10.c: New test.
>---
> gcc/match.pd | 26 ++++++++++++-------
> .../gcc.c-torture/execute/bitfld-10.c | 24 +++++++++++++++++
> 2 files changed, 41 insertions(+), 9 deletions(-)
> create mode 100644 gcc/testsuite/gcc.c-torture/execute/bitfld-10.c
>
>diff --git a/gcc/match.pd b/gcc/match.pd
>index 9d7c1ac637f..c153e9a6e98 100644
>--- a/gcc/match.pd
>+++ b/gcc/match.pd
>@@ -3949,15 +3949,16 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> /* a ? 1 : 0 -> a if 0 and 1 are integral types. */
> (if (integer_onep (@1))
> (convert (convert:boolean_type_node @0)))
>- /* a ? -1 : 0 -> -a. */
>- (if (INTEGRAL_TYPE_P (type) && integer_all_onesp (@1))
>- (negate (convert (convert:boolean_type_node @0))))
> /* a ? powerof2cst : 0 -> a << (log2(powerof2cst)) */
> (if (INTEGRAL_TYPE_P (type) && integer_pow2p (@1))
> (with {
> tree shift = build_int_cst (integer_type_node, tree_log2 (@1));
> }
>- (lshift (convert (convert:boolean_type_node @0)) { shift; })))))
>+ (lshift (convert (convert:boolean_type_node @0)) { shift; })))
>+ /* a ? -1 : 0 -> -a. No need to check the TYPE_PRECISION not being 1
>+ here as the powerof2cst case above will handle that case correctly. */
>+ (if (INTEGRAL_TYPE_P (type) && integer_all_onesp (@1))
>+ (negate (convert (convert:boolean_type_node @0))))))
> (if (integer_zerop (@1))
> (with {
> tree booltrue = constant_boolean_node (true, boolean_type_node);
>@@ -3966,16 +3967,23 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> /* a ? 0 : 1 -> !a. */
> (if (integer_onep (@2))
> (convert (bit_xor (convert:boolean_type_node @0) { booltrue; } )))
>- /* a ? -1 : 0 -> -(!a). */
>- (if (INTEGRAL_TYPE_P (type) && integer_all_onesp (@2))
>- (negate (convert (bit_xor (convert:boolean_type_node @0) { booltrue; }
>))))
> /* a ? powerof2cst : 0 -> (!a) << (log2(powerof2cst)) */
>- (if (INTEGRAL_TYPE_P (type) && integer_pow2p (@2))
>+ (if (INTEGRAL_TYPE_P (type) && integer_pow2p (@2)
>+ && TYPE_PRECISION (type) != 1)
> (with {
> tree shift = build_int_cst (integer_type_node, tree_log2 (@2));
> }
> (lshift (convert (bit_xor (convert:boolean_type_node @0) { booltrue; }
> ))
>- { shift; }))))))))
>+ { shift; })))
>+ /* a ? -1 : 0 -> -(!a). No need to check the TYPE_PRECISION not being 1
>+ here as the powerof2cst case above will handle that case correctly. */
>+ (if (INTEGRAL_TYPE_P (type) && integer_all_onesp (@2))
>+ (negate (convert (bit_xor (convert:boolean_type_node @0) { booltrue; }
>))))
>+ )
>+ )
>+ )
>+ )
>+)
> #endif
>
> /* Simplification moved from fold_cond_expr_with_comparison. It may also
>diff --git a/gcc/testsuite/gcc.c-torture/execute/bitfld-10.c
>b/gcc/testsuite/gcc.c-torture/execute/bitfld-10.c
>new file mode 100644
>index 00000000000..bdbf5733ce7
>--- /dev/null
>+++ b/gcc/testsuite/gcc.c-torture/execute/bitfld-10.c
>@@ -0,0 +1,24 @@
>+/* PR tree-optimization/102622 */
>+/* Wrong code introduced due to phi-opt
>+ introducing undefined signed interger overflow
>+ with one bit signed integer negation. */
>+
>+struct f{signed t:1;};
>+int g(struct f *a, int t) __attribute__((noipa));
>+int g(struct f *a, int t)
>+{
>+ if (t)
>+ a->t = -1;
>+ else
>+ a->t = 0;
>+ int t1 = a->t;
>+ if (t1) return 1;
>+ return t1;
>+}
>+
>+int main(void)
>+{
>+ struct f a;
>+ if (!g(&a, 1)) __builtin_abort();
>+ return 0;
>+}
